With the advancement of epitaxy technology and reduction of manufacture costs, use of light emitting diodes (LEDs) has been gradually introduced to various fields. For example, LEDs have seen use in electronic devices such as mobile phones, multimedia players, PDAs, etc. It is expected that such use will be expended to the general lighting system to replace many conventional lighting devices.
In popularizing the use of light emitting diodes, one important issue, among others, is to increase the lighting efficiency of LEDs to a highest achievable level. Given that, reducing absorbance and attenuation of light generated by LEDs would be a critical area for improvement.
In a conventional LED structure, a metal reflecting mirror is used to reduce light attenuation and increase lighting efficiency. For example, in manufacture process where silver paste binding technology is replaced by eutectic, because the gold/tin thin film used tends to absorb light, hence reducing lighting efficiency, a metal reflecting mirror is used at the back side of a LED to lessen the extent of light absorbance. Referring to FIG. 1, a lighting device 100 of conventional technology is shown. The lighting device 100 has a light emitting diode structure 110, a titanium (Ti) layer 120, an aluminum (Al) layer 130 and a gold/tin (Au/Sn) alloy layer 140. In the conventional lighting device 100, the titanium layer 120 of thickness around 10 Å (angstroms) and the aluminum layer 130 of thickness around 2000 Å are used as a metal reflecting layer, whereas the gold/tin alloy layer 140 is used for eutectic binding process, or eutectic welding. However, in structures that employ conventional metal reflecting layers, such as the titanium layer 120 and the aluminum layer 130 shown in FIG. 1, the reflectivity rendered is not satisfactory, and particularly, the low reflectivity at the Ultra-Violet (UV) band undermines their applicability. Furthermore, the metal reflective thin film affects the reflectivity due to different vapor deposition conditions, resulting in difficulty in assuring the device quality.
Therefore, it is desirable to have a high efficiency lighting device with increased lighting and heat dissipating efficiency of the composing elements thereof.